Her health problems include dementia which seems to be progressing, rapidly. I am a very fit, physically and mentally, 90-yr-old, who would like to resume playing tennis 3 times a week as well as long-term stay travels. While we have family nearby, for various reasons, it is inconvenient for them to help out with any regularity or for long periods. I am feeling some guilt for considering memory care for her, even though I know she would receive more appropriate care. Should I feel selfish?
I don't like questions like these, because basically it's fishing for compliments. You're trying to provoke certain answers with that question.
As for the rest, your situation, you're the only one who knows what you're going through and how your wife is. You decide what's best (memory care or not), not strangers on the internet who don't know the full picture.
If it's just because you're not wanting to be tied down to caring for her 24/7 perhaps you can find an Adult Daycare Center in your city to take her to up to 5 days a week and up to 8 hours a day. They are fabulous and take great care of the folks that attend. They give them breakfast, a snack and lunch, plus keep them occupied with various activities.
Or you can hire some in-home help to assist you with her care.
That would give you ample time to play tennis, and do whatever else you would like to do.
You will know when it's time to place her. When it's best for you both.
Best wishes.
Take your life back, know that she will be safe. You can visit her as much as you like,
I wish you the very best and know that you will be making the right decision for the both of you.