@lovemyjanu, everytime someone says G-Spot is discovered in 1950s, I will keep objecting.
About this spot was mentioned in 3rd century verysion of Kamasutra. The commentator version in Sanskrit 'Jayamangala' of Yashodhara in 13 century later Hindi version by Devadatta Shastri and Sir Burton's English version in 1883 couldnot explain that. However 'Ratirahasya' by Kokka Pandit mentioned G-spot as 'saspanda. Please dont keep repeating two things, G-spot was discovered by that German guy and G-spot is a myth. Its reality and was discovered in India in 3rd century, about 1700 years before Dr. Grafenberg discovered.
Now to Land Cruiser on your question. Your girlfriend has a rough one and dont feel. It may happen, depending on the time. As per time table, night is distributed in 4 parts, 6PM to 9PM as first, 9PM to 12AM as 2nd, 12AM to 3AM as 3rd and 3AM to 6AM as 4th. Based on a girls orgasn, or lets be to the point, based on your girls vaginal depth, she can fall under one of the 4 types as was defined. Each type has different part of night to get stimulated, it can be one or more.
On usual cases, 12AM is a peak point for any girl's sexual sensitivity, it starts from 10PM keep growing to peak and then goes down at 2AM. If your girl doesnot feel the sensuality at 12AM, that would be a bit concerning. When you go for stimulating, that you havenot mentioned.
You are right on two stimulation together, go for a prolong foreplay, start with less sensitive erogenous zone to moderate zone to most sensitive zones, on fial stage go for using fingers on her vagina and lips and tongue on her clit, that should do the trick. In rare cases her A spot is real triggering point, in that case G-Spot gets lower priority.
Anyway, knowing this two info could touch base better, one is her vagina type, the depth and the other is the time you go for sex.