Kindly ask her to get used to your alarm sound, and not wake up then.
This may seem harsh, but actually it isn't. Every house has it's own specific sounds, and it is quite normal to get used to them and not wake up. If you hear other sounds that are unusual, then you wake up. It is a natural thing.
I had a roommate in college that had trouble waking up even with an alarm, and had a much earlier class schedule than me. Never got used to it, just got sleep deprivation. Maybe it's "natural" for you and my ex roommate to sleep through alarms, but as they are designed to not let you sleep through them, many people cannot.
Yeah, we'll get used to the house for sure, but I'll have to be quiet for the time being. It's not worth losing what could be an extra hour or two of everyone's sleep. We generally make an effort to not shield them from noise during daytime naps and such, but sleep is too precious these days.