Susan has great experience worth listening to! There are options between spaying puppies and keeping bitches intact for life, though.
The difference between an intact male and female is mostly the risk of pyometra. The more heats she goes through, the risk escalates quickly. So, I would spay any female dog I had at some point. However, that does not mean you have to do it now. It might be more expensive if you wait, but letting her go through a few heats and mature more first is another viable option.
I have also read that some vets will take out only the ovaries and leave the uterus. This is a less major procedure, so there would likely be less pain. The uterus remains, but without the hormones from the ovaries, she will not have heats, so her risk of pyometra will not increase. Do a search for ovariectomy in dogs for more information.
If you had an intact male for his whole life without him ever managing to breed, you are likely responsible enough to have an intact female too, but pyometra is no joke. Do some reading on how to recognize heat cycles and keep a close eye on her. I fostered a dog in heat once, and I know she would have done anything to get away to breed!
First time Chihuahua owner with many years of dog experience!