It could be very dangerous in the event of a fire. Also how would she use the bathroom if she needed to in the night? Have you seen the extra high stair gates? Would it be worth getting some of those?
Have you talked to your GP? Does she see any consultant to follow up on her adhd? It is likely they have advice. If not, maybe they can escalate your referral. Also ask if an Occupational Therapist can help with this. It is not illegal but do you think she can be safe in her room by herself? We have a futton in our LO's bedroom and that is where I sleep when our LO is ill or wants to sleep with us. It helps them to feel the company but you are not sharing beds and you can manage to sleep. But this is with a child that sleeps. If she is not sleeping during the night, I bet it makes her symptoms worse during the day so it is important to find out what is keeping her up at night.
I have had a dog gate which is just like a baby gate but almost double the height x
If she's on any medication for her adhd, it would be asking for a meds review. If the meds dose is too high on a long acting med it may not be out her system by bedtime which is why she takes ages to settle or wakes up regularly at night. Also do you do any activities with her that will get her energy out before bedtime so she's tired enough to sleep?
Have you tried using a night light that goes red when its ‘time to sleep’, green light can wake up? I haven’t used it personally but people have spoken highly about it that I know It sounds very stressful