So I met a really pretty girl I had a lot in common with, at the end of my second year of uni, started dating, getting together etc. She's final year but she's doing her next degree in the same city as I'm doing my year-long internship. She's now gone back to her country for the summer, however is back in July for 10 days with her family for graduation. We also talked about me visiting her in her country in August on holiday which she seemed really excited about. She left roughly on the 10th June. She told me to try and be free on the 19th July as she's free that day when she's back. She get's back on the 9th July, I believe. I messaged her Friday saying:
Me: "Are you free any of the days before the 19th - I start work the 19th so we'll get more time together!

"
Her: "Ooh i thought you started on the 20th, we are going to {city} for a couple of days and then we are doing day trips so im not sure

but ill see and let you know closer to the time
Me: "Hmm I may have to consider a trip to {her country} then... :/

"
Her: "I think you should indeed

"
-Then she sends massive happy face.-
At the start when she went back she was messaging me (first) all day, asking what I'm doing etc telling me she misses me. However over the last week, she seems to have lost interest somewhat, not even sending me snapchats every morning like she used to.
Today I suggested we SPAM (we haven't actually done that yet) and she said;
Her: "hellouuuuu, just came home from the beach (where i think ive burnt my knees :p) and I have to get ready and then I'll leave again ;p #alwaysinahurry what are you doing? "
I made a joke then told her I might be going to Italy. She then asked why, so I replied.
Me : "There was me thinking my spontaneity was part of the reason you liked me... :/ I guess it's just my looks..."
Her : "Hahaha you're crazy! ;p"
She then followed it up with;
Her: "we have a bit of an issue for the 19th but ill try and see whats actually happening tomorrow and let you know :/ "
Me: "That's a shame. What's up?"
Her: "My nan is probably coming from {other town} a day earlier to spend the day with me before we fly out!"
I just teased her about being unreliable, but she didn't reply despite being online later. Before this she was sending me snapchats of bars with live music telling me I would love it there etc, I think perhaps I've consciously made more of an effort to reply and talk to her since she moved abroad. I was being quite sweet i.e. telling her about some things that reminded me of her sometimes to which she replied with "I miss you

" However these past few days she has responded a bit more generically. I'm sure I'm being a massive pussy over this, but I'm really worried she's losing interest. Am I better off taking a step back or will that only make her lose interest quicker?
She even made a theoretical list of all the things we need to do together when we're in the same city.
How can I reignite the spark from when we were together? When we're together everything's good, but I just feel like I can't convey myself and my personality over messaging etc. What do you guys suggest? Do you think when she gets back to my country she'll be reminded of me etc? I know she's been very busy lately.
To show it's not just soppy bullshit, last week we were talking about tennis, and me taking the piss out of her playing, then I said "I think you would look quite hot in tennis kit

" To which she replied;
Her : "I still have my skirt

"
Me: "That's the important thing!"
Her: "Exactly

So how was your day?"
So I was still keeping it flirty despite mentioning sweet things she likes.
I really dunno what to do guys, this is making me quite down and depressed.
All advice is appreciated.