Hey Felipe,
“I'm thinking”... Don't spend ages agonizing over this, just message her. Girls like her get TONS of messages so you need to get in there now.
I thought since no one has answered I'd drop my 2 cents regarding online dating. I've been doing it for around 4 months and I go on dates when I can fit them in around my schedule(around 1 per month).
Aim for a phone number within 3-8 messages, any shorter than that and it feels too mercenary. Even if she's really into you, she still wants to be charmed and seduced a little. Any longer than that and you risk falling into the "online friend zone/online pen pal" category.
Vague Structure:
Opener - Light, playful and flirty message that clearly sets a man-to-woman frame and shows you're not there to be friends. The opener shouldn't be too long...roughly 2-3 lines. The longer your message the less likely she'll be to respond. In her profile it says "I don't mind a challenge".... In which case I'd be tempted to say something like.. "You don't mind a challenge...Well here I am
"
Second Message - I personally like to qualify her.. e.g. "I really like that you're into X, Y or Z.. But I'm afraid I'm not won over that easily so... tell me a little about blah blah blah?"
Third Message - Seed the date - E.g. "You like Snooker?!.. I'll bet you drink I can kick your ass at Snooker with my hands tied behind my back(don't get any ideas! lol)" - That way if she says yes any way to that she's essentially said "yes" to a drink with you. It's subtle but it plays on cognitive dissonance. Once she's said yes to a vague idea of meeting, you can then shape into more concrete plans e.g. "When are you up for that game of Snooker? I'm free this Saturday..". If she says yes to the vague plans, she's more likely to say yes when you come to arrange an actual date because she's already agreed to do so on some level.
Fourth - Eighth Message - When you ask for the number offer your number first. It shows commitment/investment on your part.. But also it plays on the reciprocity effect, which is the idea that if you give someone something they are more inclined to give you something in return when you ask for it.
Once you have her number, make sure you text her so she has your number knows who you are when you go to text her. Nothing kills an interaction more than her having to ask "Who is this?!" when you ask to meet.
Final note: My advice would be that once you sent the message to her... send another bunch of messages to some other girls. Once you have load of other girls messaging you, you'll naturally be less needy with this current girl(e.g. Checking to see if she's replied all the time).
Best of luck! Keep us updated!
BonJovisMother