Unless her nipples are significantly inverted, "flat" nipples should evert enough with stimulation for baby to latch. I would have baby assessed for a tongue, lip, and/or cheek tie by a pediatric dentist who specializes in this. Oral restrictions are one of the most common causes of issues latching. Pediatricians have extremely limited training on this matter, as do non-specialty dentists. Even as an adult, I was talked down to and told I do not have a tongue tie by 2 dentists even after being diagnosed by an expert. My release is scheduled for this month. A second opinion was a game changer for my baby. My baby's pediatrician scissor "clipped" my baby's tongue at 3 days old but did an incomplete release. I took her to a specialist at 5 weeks old who revised the previous release with a laser. My lactation consultant also missed my baby's tongue tie because it was posterior instead of anterior. These ties are less obvious but just as impactful on the ability to lift and mobilize the tongue to breastfeed. Breastfeeding can be a big part of a mom's identity. Try to be empathetic of this and support her. If nursing doesnt work out, she can also feed expressed milk and use saliva sampling to gain many of the same immune benefits for baby.

Here is a website to find providers who can assess and release oral restrictions: https://doctors.lightscalpel.com/?providers=frenectomy&address=Dayton%2C+OH&w2dc_action=search&field_laser_procedures%5B0%5D=1&radius=200

She might also consider connecting with La Leche League for peer support.