I would really think hard about it. Is it worth it, if something happens to her. My 7 yr old for all the reason you think of to make it okay, ended up with a ruptured uterus and almost lost her. The worse thing I have been through in 30 some yrs of breeding. She had whelped easy, but litter before was 10. So who knew I was pushing things and for what ?
Just know that the odds are going in the wrong direction with age. Twice I bred older girls. The first one had 2 puppies. One was tiny and did not survive. The other had a heart murmur. The second girl bred at 7 had one puppy seen on the ultrasound. It did not make it to term, so there were no puppies.
As you can imagine, I would not do it again. There is enough heartbreak without tempting fate. Just my experience.
When I bred my 7-year old bitch who had previous easily-whelped litters, she had her biggest litter - 10 puppies - all free-whelped, lost the last one, but the remaining 9 were just fine. Her mom had a large litter of 12 at almost 7 years old as well.