I moved in with mom about 5 years ago to care for her and the home. Now we need a new roof. The contract and price freaked her out! (Yes, it's expensive, but all roof jobs are costly.) Now she won't sign the contract. I think I'll be stuck with buckets again this coming winter. I tried again this morning to get her signature for 45 minutes by calmly reviewing the contract and pointing out the problem areas. To no avail. Boo hoo.
Plus I updated my very old POA's as I had my parents as my POA... good heavens, that would no longer work at their stage of life, so I had to appoint new POA's.
If you don't have legal authority, take a different tact and approach her in a way that won't make her comfortable to get that authority.... perhaps have POAs created for you so that you have succession in place, and tell Mom you want to ensure that she's covered as well.
You'll have to gauge how to do this gently so it doesn't frighten her into thinking that she might be left alone if something happens to you.
The important thing is that if the roof is bad enough to be replaced now, waiting longer is really gambling on much more extensive damage.
But I wouldn't take just one estimate. As Jessie observes, estimates can vary significantly. See if you can find out from your local building and inspection department if there are any roofers that work consistently in your community. They shouldn't be recommending, but asking for prevalent companies isn't a recommendation.
I prepared my own work breakdown description and gave it to contractors to bid, so they were all bidding on the same project. I did this after finding out that some of them watched HGTV and DIY Networks and came up with elaborate proposals for what THEY felt should be done. They wouldn't factor out just the necessary work, so basically their estimates were worthless (and their approach removed them from consideration.)
Check with your state's licensing departments to see if roofers have to be licensed, and if so, see if you can get a list of those who are. Ask for references. If they balk, that's not a good sign. And be aware that some contractors will fabricate references.
Contact your local senior center and see if any companies have notified it that senior discounts are available. Also contact the community, perhaps building inspection, to find out if HUD grants are available to income qualified seniors for emergency repairs. Habitat for Humanity and Christmas in April, as well as some local churches, also do some gratis work, again for income qualified people.
Research and find some online DIY forums; find the roofing section and read up on what happens if the roof is leaking or in less than good shape. Water penetration can as FF observes cause rotting damage, mold growth, insect (especially ants) attraction, and more. If there's old paint, pre 1978, peeling paint could cause the possibility of lead release, especially if there's an actual roof leak which is creeping down and affecting plaster walls (I had that problem - it's an awful mess).
Speaking from experience, when I think of all the things that could happen to my own house, it becomes overwhelming, so I have to back off and focus only on the primary issue. I would do that if I were in your place, and that primary issue is finding a way to get the roofing done, by a contractor with whom you feel comfortable, andto take the burden off your mother.
My mother has a hard time with the cost of repairs now, too. She remembers the prices from last century when they were a fraction of what they are now. If the roof needs replacing, though, it is important. Water damage is very costly and can destroy the walls. Roofs to me follow Franklin's Law "A stitch in time saves nine."
Sometimes things such as roofs, plumbing, electrical work is overwhelming to a person who never did hands-on repairs him/herself. Your Mom doesn't understand that water leaks can create many other problems if they go unfixed. Such as electricity can short out.... wood structures in the attic will start to rot and lose strength, etc.
My Dad use to balk at getting things repaired at the house. Now that Dad wants his house sold, he is ready to finally open up the vault and pay for repairs. I notice he will say yes quickly if I use tradesmen that he had used and liked in the past.