Well, a 'bulky uterus' with that being the only thing found isn't usually a reason for miscarriage. If they found other things that 'made it bulky' that should be noted on the report like fibroids, endometriosis, adenomyosis, etc. Those things may interfere, but just a bulky uterus is vague and likely not to pose a problem if that is all they say is going on. You should ask the doctor the reason for the bulky uterus and to look into it further. More testing. I'd also want lab work to see what her hormone levels are and if they need to be adjusted.
It takes most couples on average at least a year to conceive once they officially start trying. Has she been seen by a doctor? She's having multiple miscarriage. No trouble getting pregnant but not staying pregnant. She should be evaluated by her doctor to see if there is an anatomical issue or hormonal or something like that and most things can be remedied.