Hi OP. I think the reason your cleaner is slow, is because she has to be to make herself look busy for 8 hours.
I understand how she could possibly be 8 hours if she was going on a long dog walk and changing 6 beds, plus maybe an hours ironing. However, she can't be changing the beds twice a week. Also, you sadly no longer have your dog.
The result is, she is spanning tasks out to fill the time.
My cleaner comes for 4 hours twice a week and it's a similar sized house. My three kids are still at home, but spare bedrooms and bathrooms only require a very quick dust weekly.
My cleaner does not deal with laundry or beds. I could add an extra hour on for this each time, however, it's cheaper to get shirts steam pressed - I think it's about 50p per shirt, so compare that of the cost of your cleaner's time if she's ironing (slowly)!
If I were you, I would either find her more to do or renegotiate hours now that there is no dog and only two of you in the house.
Also, 8 hours is too long for someone to be doing constant housework. Would you do 8 hours non-stop? Realistically, you get more out of people in shorter bursts of activity.