I find it helpful not to assume an agenda for the dog - we can never truly know what her intentions are - and, regardless, management is your best option. If it's easy to disengage her from your pup as it is, I would keep doing so (you can always have her drag a short leash so that you can gently re-direct her). Keep them separated when you are not around so that she never has the opportunity to mount her outside of your supervision, this will continue the behavior.
With a little time and patience this problem will solve itself. Once the puppy hits adolescence she will very likely start retaliating (as an adult would) and it should stop.
Spaying will also probably help.
I know it's a bit of a frustrating and silly problem, hang in there
Here are a few articles that deal with dominance theory, maybe they will also be of some interest?
http://www.dogwelfarecampaign.org/why-not-dominance.php
http://www.theotherendoftheleash.com...d-as-dominance
http://www.nonlineardogs.com/socialorganisation.html