I can make some logical guesses....
Why does Shining Finger want the IBM 5100?
Simplist reason (And it's the one thing we know the IBM can be used for), use it to read that special data type that SERN uses.
Why is the Shining Finger so interested in the Time Traveling?
Again simplist reason which ties into why she wants the IBM, like Obake, she has somehow gained acess to SERN's data on their servers and hence she'd need the IBM just like Okabe and co did.
Why did the Shining Finger take random pictures?
1) a form of OCD 2) to further her agenda 3) no idea =/
Why does the Shining Finger constantly text Okabe instead of talking to him?
I have a possible answer, bear with me, it's gonna be a bit of a long one.
With my new theory I have going I think it's because she perhaps suffers from something that effects her communication skills. Btw good chance im wrong here because this is a 'real world' answer and anime don't like the real world. But this fits with my theory however. Anyway, she probably suffers massive discomfort talking to people, even being surrounded by so many people is a strain on her. Texting Okabe wouldn't be as painful to her as openly talking would.
Now then, I think Shining Finger is alot like Lisbeth Salander (The girl with the dragon tatoo), so where looking at someone with communication difficulties, but also has incredible hacking skill. I think she has hacked SERN and now needs the IBM to read the data. I think in that other timeline she might have known that she would no longer have been forced into Okabes crew when her D-mail got sent off. This would suit her fine the way that she is (Dealing with others is painful to her) and I think she has no intention of joining forces. This makes her the calprit behind Okabes threats. Think about it, those images he recieved are from the SERN experiments, which she has access to.
To what her ultimate goal is I have no idea. But if I'm right about her having a condition like I described then the very fact shes always wandering the streets has great significance. If being around people was painful to her then she has a very series objective which she's not letting her pain get in the way of. Thats what u call focus and determination.
Theres one thing I have no idea about......what the heck was the real purpose behind the D-Mail she had sent out? There's no way it didn't serve some purpose in her agenda.