Maybe she is a High Sleep need child & just does like to sleep. My DS1 was still on 3 naps/day until 9mo & no way did he do 3hours A time at that age, pity my DS2 was the opposite LOL
I used to take my boys on walks around the garden, & house showing them things etc. I am "old school" in that I hate walkers & jumpers & things like that & go with "if it was around 2000 years ago then that's what nature intended" so my children spent lots of time holding balls (maybe that is why they throw & catch well now LOL) looking at books & things that worked on hand eye coordination rather than anything else.
Is she crawling & moving yet (my DS1 didn't until 10.5months) because if she is then really that is the best thing to let her be entertained, to just crawl around, if she isn't tummy time with a toy in front etc... really the sitting & the tummy time are the best "activities" at this age as they start to work on the movement side of things. Also anything that is hand eye has major long term benefits, so clear plastic balls that have something inside that they can look at are great... but really that crawling side ie tummy time, sitting up etc are the best options.