My mom has had 3 occurrences of bed bugs.

Oh wow. So sorry to hear about this. Your poor mom. I hope you are able to get rid of the bbugs for good this time.

Been thru this problem of bed bugs with my dad. Severe infestation, months of spraying... did not use the heat treatment because of how old the trailer was ...it wouldn't have worked. After Six months of treating his home he had a stroke which landed him in the hospital. Sitting beside him I saw one crawling on the bed sheet...inspected his clothes and hat all packedup in the hospital I found a nest in his hat, they were in his shoes, and the collar of his shirt! A big querentine in the hospital happened... had to contact the ambulance service at transported him there ...was a nightmare to say the least. Dad bought a hospital bed at an auction and he claims that's where they came from ....that we will never know  where they came from probably ....he is legally blind and cannot see how bad the situation was in his home.
He also had home helpers come in weekly and they could have very well carried one of these nasty little creatures home with them.  True one of them could've brought it in I don't know !?!? His friends would come pick him up to go to town and I had a fear of him transferring one in their vehicles... or did he pick one up from their vehicle, I will never know ...everyone who he had contact with who came in his home or whoever's vehicle he was in I had to tell them to treat their vehicles and inspect their homes. we live in a tiny little town with the usual coffee shop and I was told a bedbug was seen crawling on his shoulder at the table. He got numerous bites from them and I think he has PTSD because he thinks he still has bites and constantly looks for bugs at assisted-living. These nasty little creatures can live forever and they multiply like crazy ...go through incubation periods which requires months of treatment and gets very costly.
But I'm here to say is, just because you had workers come in there does not mean they are the ones that brought them to your mothers home. If they're home gets inspected and they are found there does not mean that's where the whole problem started...these little beasts are great sneaky travelers... they can even be picked up in the waiting room at a doctors office or sitting in a restaurant !!!!! Etc etc etc!!!!!
When the bedbug problems started with my dad my husband went in with a hazmat outfit on and took all the precautions and still brought one home to our home !!!!! I even made him strip down in the middle of January in the snow and disposed of everything he had on ! One month later my son found a bed bug crawling on the pillow on the couch !! Immediately at 1 o'clock in the morning I started flipping everything over inspecting and I'll be damned found a nest in my husband's recliner and more in a brand-new couch we just bought!
Everything got wrapped in plastic drug outside and burned!! Tons  i'm watching every single blanket in my house and I have hundreds of them, pillows shampooing carpet re-washing clothes constantly I went out of my mind   Months of treatment and very costly but thankfully I caught them in their beginning hatching...yuck. I hate them I think I have PTSD too so do my kids.
You can be the cleanest person in the world and still get bedbugs!
If you have been in your mothers home you really need to check out your home too or if she has been in your vehicle.
Also shopping at thrift stores can bring them home too.

I don't mean to scare you about your situation is just it's very hard to get rid of these creatures and realizing how easy they travel so many ways How do you nip the problem in the butt??    inspecting every little corner in the house, washing clothes in hot water and hot dryer they can hide in the tiniest little places and lay eggs and lots of them. My dad even had evidence of them in his wallet, they are called casings. I had to wash and spray a solution on all his money and important cards I disposedof his new wallet!   Was not willing to take any chances !
You have any questions just ask I have lots of suggestions like what I did to get rid of them in my home.
My dad's living conditions and the condition of his trailer was so bad we had to bulldoze it in and burn everything. I went in with the hazmat outfit on trying to salvage important papers in a few sentimental items but it has really caused me great grief and nightmares. It was so sad to know my dad had been living like that and he is my neighbor, when I would visit him he would always meet me outside or visit on his porch... The stroke was kind of a blessing in disguisebecause that got him out of his home into the hospital  and his terrible living environment ...then he needed extra care, was able to get him in assisted-living.  Now  seven months later he wants to come back hometo a new little cabin my husband built for him. ( my husband felt terrible because we had to dispose of his home and he promised Dad to rebuild something new, we realize now we shouldn't have acted so fast to rebuild) I'm in the process talking with dad, discussing why he needs to stay where he's at... if he comes back home his living conditions will continue as they were if not worse. I know I can't take on his care on my own, he's never been willing to do what he needs to do for his own health ever let alone now

Where are you finding the bedbugs?
are you finding casings?
Bedbugs like to come out at night to feed on blood because they are hungry... and they go back to hide, mate, lay eggs.
Look in your mom's purse, shoes, everywhere she sets, sleep, I even found a nest behind a picture on the wall.
Itching right now, but please remember these nasty creatures could've been picked up anywhere and you will probably never know where.
I will be thinking of you and just know that the situation does get better but you need to attack it like a warrior!!!    They can be in the cleanest of homes !
Please let me know how it's going!!

Bella

another thought, if you do suspect the home helpers, maybe they picked one up from another person they care for somewhere else and brought one to your mom's home !?!