If you aren't going to breed her (and that means having a breeding plan, and having the funds to cope with that because anything can go wrong with pregnancy
and birth especially with a tiny dog
)....then get her fixed. You would honestly, be doing her a favour.
Pyometra is very common in unspayed females as they grow older. My gosh! Pyometra is scary. My dog had it, had to have emergency surgery, survived and did OK after, but many times Pyometra kills -and very quickly too.