There are many, many good 9mm pistols out. The constraints of OP limit them quite a bit.
Women’s hands are smaller, and what works for most men often doesn’t work for them.
The S&W options tend to be favored by women, at least in my experience. The Shield EZ might be another option, although it is more difficult and less pleasant to shoot than an M&P.
The PDP F series is a much more expensive option specifically designed for female hands. The HK VP9 is another much more expensive option that often works well for women.
The key is to find something that fits. If she feels good with the SD9, get it. If the RXM fits better, spend the extra money. If an M&P compact with a small backstrap works best, it’s the clear winner, etc.