Sit her down, try asking her if she's ready

Sit her down, try asking her if she's ready, what does she thinks about it... But don't ever, EVER try having sex with her just like that, it can be considered as rape. Just ask her straight, tell her you won't do anything she doesn't want to, be gentle and go by her pace. Be caring and loving, she will appreciate it so much even if she won't agree right away. Don't push her, if she says no then it's no and tell her that you'll wait till she's ready :)