Can you recommend a tree that flowers during August to plant in the local Cremetorium in memory of a friend, who died of cancer. to commemorate her birthday.

Trees don't grow to 8' then stop, I'm afraid. Why not consider a flowering shrub - there are Hebes that flower during late summer, or a Cistus maybe? Or how about a late-flowering rose shrub? You might even be able to find one with her name!

Other possibilities: Lavatera, Buddleja, Hydrangea.

Good luck.

Buddleia Nanho Blue might be suitable it is a dwarf form, which in Buddleias means 6 to 8ft., and can be kept pruned if necessary without suffering.

Forgot to add Ceanothus - there are some that flower in August. Lovely blue, and could grow a bit tree-like if you choose the right one.

Yes, agree that Ceanothus is a lovely, large plant with proper blue flowers.
Just dont' try and cut it back because it won't like it and may not survive.