If you're vegetarian then you presumably still eat eggs and dairy? That gives you a lot more low carb options than vegan, but vegan is still possible.
The critical thing is how insulin resistant she is. If she's insulin resistant then low carb seems like a good idea, because her body can't cope with carbs and insulin just makes things worse. But if the issue is lack of insulin then insulin is her best friend and is really not the end of the world. (I've been taking it for 51 years and though there are aspects of T1 I hate, hello hypos, insulin has kept me alive and well and I am a big fan.
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