Baby monitors/camera in general

So we have our August 3 year old, and another baby on the way, I'm 30 weeks soon, so my 3yo is moving into the larger double bedroom of our house, where so far she has been in the smaller box room/nursery before this new baby comes. Her big girl bedroom will be finished this weekend and she is very excited, she's been sleeping in a normal single bed for ages so no issues with that, my issue is, the baby monitor we have been using is fixed to the wall in the nursery. So it makes sense to keep it there and use for the next baby once it starts using that bedroom in future, however my 3yo does still wake in the night and her pattern is not consistent. Sometimes she will go for 2 weeks with no wake up, and sometimes we will spend 2 weeks with her up every night, some of those night she soothes herself, some she let's us put her back to her own bed and some she gets into bed with us. The whole thing is a very mixed bag. So we do still use the baby monitor with her cause we wanna know if she's awake, or stirring, or halfway out of bed or if she looks like she's just gonna go back to sleep alone. Also my partner often works nights so I check her camera randomly to put me at peace that she's asleep before I go to sleep myself, or jump in the shower, or start something downstairs where I won't hear her (like vacuuming or something) It just eases my peace cause I'm the only adult in the house. Do I buy a new camera for her big girl bedroom? Or get a dual camera? Or is 3 too old for a camera? I feel like if she just got in bed and slept I wouldn't have an issue, but because it's always different week by week, I'm not sure if I would be able to rest easy without one