Hi Marian
1. You are definitely not alone - I think most people that seriously look into genetic genealogy discover an NPE or 3!
2. Biggles50's suggestion of uploading to GEDMatch and MyHeritage is excellent - MyHeritage is infinitely better than Ancestry for European matches (simply because more Europeans use MyHeritage than Ancestry). My mother is Dutch, and her Ancestry matches are pretty paltry, but her MyHeritage matches are particularly rich and far surpass any of my British relatives.
3. I'd like to give a bit more of an optimistic response than Biggles50, to balance things out. Two of my grandparents were the results of NPEs, i.e. the same situation as your mother. For one it took a few weeks, for the other it took a few months, of research to identify who I thought the father was likely to be. Both were then confirmed by closer relatives identified on those branches (e.g. first cousins) taking a test, which confirmed the relationship. I was lucky in that one of those fathers was the only son in his family of 12 sisters, so he was the only potential 'culprit'!
I have even identified (with as strong confidence as possible this far back) the biological father of my illegitimate great-great-grandmother. This took a great deal more work, and although I knew the broader family he came from, it took several years before I had identified the specific member of that family who was the father. I knew he was likely to be the grandson of Michael & Jane, born in the late 18th century. They had a dozen or so grandsons. But then finally I linked my DNA to one of Michael & Jane's daughters-in-law: so the mystery father had to be one of their sons - and they only had one who was still alive at the relevant time. Huzzah!
Take things one step at a time - upload your Ancestry results onto MyHeritage, and see what happens. Please remember you don't need to buy a new DNA test, you just have to download the raw results from Ancestry and upload them to MyHeritage. It's free. Let me know if you need any pointers on how to do that.
