For Riviera Maya:
Honestly, if your buddy does not dive my suggestion is, in case that you have reserved in a resort, to be sure there is a dive center in it, so that you will be able to go for a dive just 2/3 hours and meet her afterwards even in the beach -perhaps while she is taking a tequila : ) - i.e. Bahia Principe Tulum resort and bahia dive center (also known as bahia divers). Or Akumal beach resort and Mr Diver Dive Shop. Almost all provide reef dives, cenote dives, and cozumel dives
Ask your resort, almost all have a dive shop or a dive center able to pick you up in the hotel entrance.
In case you have reserved in a condo, etc...there are dive centers that pick you up, and return you back after diving.
For reef diving you can call Akumal dive adventures:
http://www.akumaldiveadventures.com/ (not very sure of transportation but they seem to be great in reef divings and even scuba diving courses). In this case "Vista del Mar" is very close to them.
For cenote dives you can call "Diablo divers" in "Puerto Aventuras.
But I highly recommend in your case a resort if possible, i.e. Bahia.