I’m taking my nearly 5 month old camping, with 7 degree overnight temperatures expected. I’m going to layer her up and put her in a warm love to dream swaddle for sleeping. I’m conscious of her head/face getting cold. Would it ever be ok for me to put a beanie on her while she is sleeping to help keep her warm or still a definite no even when really cold? If no do you have any other suggestions to keep her warm enough?

Red Nose recommends the use of extra layer of clothing for warmth, rather than sleeping baby with a hat/beanie.
A hat or beanie could also become loose during sleep & risk covering her face.
While there may not be a risk of overheating in this specific situation, the concern about face covering may still occur.
The feel of baby’s head/face/hands/feet is not a good indication of whether baby is warm enough.
How hot does the baby feel? A good way to check baby’s temperature is to feel baby’s back or tummy (don’t worry if baby’s hands and feet feel cool - this is normal).
https://rednose.org.au/article/bedding-amount-recommended-for-safe-sleep

Red Nose has the following information about bedding -
Red Nose recommends that you, as baby’s parent or carer, use your own judgement, taking into account factors such as where you live (climate, whether it is summer or winter), whether you have heating in the house, and whether baby has a cold or minor illness (which may cause their temperature to rise)
Dress baby for sleep using layers as you would dress or use layers yourself: to be comfortable, neither too hot nor too cold - add/remove lightweight blankets to ensure baby’s chest feels comfortably warm to the touch
A good way to check baby’s temperature is to feel baby’s chest or back of neck, which should feel warm (don’t worry if baby’s hands and feet feel cool, this is normal).
Ensure baby’s head is uncovered - no hats, bonnets, beanies or hooded clothing.
https://rednose.org.au/article/how-much-bedding-does-baby-need