Hi,
I don't have experience in sensory issues, but my daughter started her periods aged 8 (we then medicated her until she was 10), so I know something about the emotional impact. It went well for us. We very much conveyed the message "puberty is normal, everyone goes through it". In our minds we separated her physical development from her emotional age and treated her according to her emotional age. We still let her be a child and eg. let her share a bath with her sister as long as both were fine with it.
My goal was that my daughter would feet happy and confident about her body. We had conversations about her friends and how far along they were and they had conversations about it too and felt they were in it together. In her circle of friends it was the late bloomers who felt awkward. I was always very explicit and very positive about it and tried to make it fun by joking around. I wanted her to know that she could bring up any worry or question. That worked well for us.
It is harder with periods, particularly when they are painful. I think it is important for girls know the what is going on and to know the practicalities, what to expect and to always be prepared. I would try out different pads (different thickness, length, material). You could also try period pants or reusable cloth pads. I would get her a pretty little bag for the pads or a pretty box to store them in. My daughters like tracking their cycles with an app. Clue is a good one.
There are quite a few good books out there, also for younger readers, which was very helpful. Babette Cole"s "Hair in Funny Places" is a good starting point. It is very short and does not give much detail. I also like "Does this happen to everyone?" I really like the humour in the pictures. The texts are geared towards older children. We also had "What's happening to me?". There are many books out there, so I would have a look around and see what you think will suit your daughter best.