If you want to buy a lingerie set for her then you should be aware of her size otherwise she cannot use it and she will look bad in her that lingerie which does fit her properly so ask her about her features and then you can buy it from store or online too as now a days there is a good option to buy it online and you will have a lot of selection out there.
If you are unable to bring her to the orgasm through your penis then you should use finger on her, do a lot of foreplay, oral sex and use sexual toys on her to make her satisfied.
If you have a problem to lick her down there because of the smell then ask her to wash her vagina before sex with plenty of water so there is no smell anymore. However, you will find odd odor there as it is natural when she starts oozing her juice from her vagina but I do not think that is too much smelly or you cannot bear it. Initially you may feel bizarre to bear the smell but with time you will become okay and you will be able to lick her as long as she wishes and you will feel good to lick her vagina as that is something most of the med do enjoy and want to spend all the time between women’s legs since you have an opportunity, make the best use of it.
You have to show some willingness to carry out her wish as you should not forget that she has been spreading her legs to get satisfaction and not any kind of relationship so her sole motive behind is to please her vagina. One thing you should keep in mind that if you are unable to satisfy her then she may stop having sex with you and she will be forced to find another penis to replace yours so give your best effort to make her happy.