For more information: https://hpets.org/index.php
A dog normally carries more weight on the front legs than the hind legs, about 60/40, and dogs usually do fine on 3 legs. I don't think there has been a large breed senior amputee here recently, but you could try posting a reply in any topic on the forum, and if the person who posted the topic has email notification they will be notified of your reply. You may also find someone currently going through the same situation on Tripawds.com.
If your dog eventually needs it, they make both harnesses and wheelchairs for amputees so you can go for longer walks. Here are examples:
https://tripawds.com/2008/04/29/new-ruf ... available/
https://www.walkaboutharnesses.com/prod ... ee-harness
https://www.handicappedpets.com/slings- ... y-support/
A DIY solution may be all you need:
If you notice slippery floors are an issue, you may want to get some mats or runners to make it easy for her.