If I may.
You may be concentrating to hard on 'down under' when alot of this is also in her head. It sounds like she may have been shuttered in the whole 'sex etc is dirty' non-sense which is all to common. Start with a position that she can confirm feels like it works for her (on top I find is good for ladies) then when it starts getting steamy get her to think about her most erotic fantasy and if possible disclaim it to you during the event, then if possible play along verbally. Its her mind that is going to push her over the edge and OOOOing in no time.
You may be concentrating to hard on 'down under' when alot of this is also in her head. It sounds like she may have been shuttered in the whole 'sex etc is dirty' non-sense which is all to common. Start with a position that she can confirm feels like it works for her (on top I find is good for ladies) then when it starts getting steamy get her to think about her most erotic fantasy and if possible disclaim it to you during the event, then if possible play along verbally. Its her mind that is going to push her over the edge and OOOOing in no time.