Large young Dog pounces the Small older Dog?

I have a big young dog that loves to pounce on our little older dog. Both are female. In dog years it is a 7 year old Great Dane/Boxer mix with a 91 year old Maltese. We are constantly having to protect her because she can’t play like the big dog can. How can we stop the big dog without breaking his spirit. I know she is just trying to play – or some of it may be jealousy but both dogs are really sweet and we give them both attention – it is just that the big one has more energy and wants to play rough!