I suppose if your daughter won't eat fish, she won't eat liver either : )
Infant formulas are supplemented with only DHA. No one seems to have complained much about the missing EPA, though these new formulas failed to produce the full results they had hoped for (and chemical residues from the development method causes diarrhea in some children). The brain uses something like 97% of fatty acids as DHA, making it sound pretty important in infants.
EPA is used to build DHA in the body, but it's also used to create some other things and it has powers of its own. Studies generally show benefits from supplementing both of these omega-3s. The body can make EPA from the vegetable precursor ALA, such as found in flax and other foods, but of course the theories are that we don't make optimal levels on our own (and some do better than others). Studies support that direct consumption of both EPA and DHA provides good benefits to all ages.
I recall some early articles suggesting some kind of negative from much EPA in infants and I think that's how the DHA-only supplementing idea began, but I'm unable to find any references to that now (anyone??). Apparently it wasn't science journal studies or they'd still be there. I think that possibly the formula companies brought this concern up because they were having enough trouble just trying to add DHA. But that's just my own conjecture. This concern about EPA in children hasn't persisted anyway as there's no published evidence that I can find now. EPA is sometimes thought of more for older-person type things, like for reducing heart disease, depression and schizophrenia, but again, it's used at all ages.
If your daughter is eating eggs, she'll be getting some EPA there, as you know, and she'll also be making some herself. You might spend the extra money to purchase the higher omega-3 eggs that come from hens fed higher precursor diets, if not giving an EPA supplement and she's not eating fish. True free-range hens make good amounts of DHA and EPA naturally from eating bugs but typical "free range" chickens really don't have that access, and then many "health" eggs say "veg-a-fed," so that's not bugs either. Some hens from small, local, organic farms may have true ranging.
I think the BrainStrong is a great supplement for your daughter. If it were me, I'd probably go at least occasionally with the gummies that have both.