One of the suggested causes of SIDS is that babies fall into such a deep sleep that they 'forget' to breathe. Although breathing is a reflex your dd has only been doing it for 21 days, and before six months reflexes are still developing.
The reason for the guideline is partly because it is believed that by sleeping ALL sleep in the room you are in any that it is never quiet enough for them to slip into that deep a sleep.
Research has also shown that babies regulate their breathing by hearing yours - another reason for all naps to be taken in the same room. Not being able to hear you, even when asleep, can cause their breathing to stop.
The reason that it is ALL sleep and not just at night is because babies don't just die at night. They die of SIDS during naps too.
Having had two babies in my family due from SIDS, one overnight, one around 11am, both in their cots in their own rooms, there is no way I would ever even contemplate this.
The babies who died in our family, and every subsequent baby born have all been studied as part of the research.
The research doesn't just look at what things evidence prevention methods, they also look at the dead babies and the circumstances that surrounded their deaths.
Research has shown that putting babies under six months to sleep in another room, be that nap or night, increases the chance that they will die.
Have you considered the fact that your baby may seem 'more settled' because she's very deeply asleep....
If you are not sure contact The Lullaby Trust (formerly the Foundation for Sudden Infant Death) and take advice from the body who research why babies die. There's a reason why they have tagines such as 'sleep safe, sleep sound, share a room with me'.
I'm sorry, I don't know who's advice you are following, but I do know based on specific, world wide SIDS research you are increasing your child's risk of SIDS.
Surely it's not a risk worth taking?