Resist, and warn her.

"Lor..." you gasp, on the brink of climax, "I'm cumming..."

She shudders as her own orgasm stretches on, but she hears your warning and lifts herself off of you. Still shaking, she bends down between your legs and points your twitching cock towards her just as your semen shoots out, splattering her face with your hot, sticky sperm. A second, smaller orgasm strikes you, and she points you towards her breasts, letting your next load spray her tits.

You groan as she jerks the last of your load out onto her tits.

She comes down from her own orgasmic peak and giggles. "I'm all messy!" she says. "I'm going to take a shower, and then more fun?"