I'm with Phil. Sixty-four isn't really senior status these days
Like others have said, try out as many guns as you can, especially when it comes to handguns. Can you find a friend who has a collection you can test? Or a range that rents different guns?
In my experience, these are the things I look for in a handgun. They are pretty female-specific:
1. Caliber: Higher calibers mean better protection, but harder handling. Experts will tell you .380 is the minimum you should carry, and generally vouch for 9 mm or .40
2. Size: The larger a gun relative to its caliber, the easier it is to handle. In other words, a really big brick of a .22 is going to feel like shooting a BB gun. Soft and easy and you can do it all day. A tiny large caliber gun, like a super-compact .40, is going to hurt your hands and be hard to aim, because there is no frame to absorb the shock. Your hands and arms get it all. You can carry it, but you won't want to practice with it.
3. Style: There are advocates for semi-autos and revolvers. There are pros and cons to each. I prefer the semi-auto.
4. Brand: There are also lots of brands. Everyone makes the same kinds of guns, just higher or lower quality, more or less features. The exception is Glock. For the most part, all Glocks are larger caliber weapons. They all operate the same way, are virtually indestructible, simple, and have NO safeties. I think they're awesome weapons for self defense, but haven't met one yet that my delicate hands could handle. They are all too big for me, even with reduced grips, and the kick isn't something I would like to experience on a regular basis.
I carry a Walther PK .380. Even at full-size, it's an easily concealable gun. The caliber is on the lower end of the spectrum, but it's easy to shoot and I can control it. I'd rather be in a situation where I have to put multiple controlled rounds into an attacker, than trying to handle some beast of a cannon and hoping I just get one good placement. I went through a few guns before settling on mine. So if you have that ability, I suggest the same.