CF alert @viccat YANBU and tell her you are working away quite a bit and unpredictable hours and days, so cannot accommodate her as there is no guarantee you will be here/there when she comes.
I had something similar about 30 years ago. I had a penpal in North America, who I wrote to for about 6 or 7 months. By around the 7th letter, she rang me (she asked me for my phone number a couple of letters back,) and said 'I have some exciting news!'
I said 'yeah?' She said 'me and Steve are comin' to the UK to stay for 2 weeks.' I said 'oh lovely, we will be able to meet up!' She said 'meet up?! Are you kiddin? D'ya know where we're staying?' I said 'no' thinking she was gonna be 100s of miles away. 'YOURS of course!' she shrieked gleefully.
She already knew I had a 2 bed flat with DH, and no kids at the time, so I had NO excuse. 
I said 'when?' She said 'next month. Around 3 weeks time, 17th of May! I simply can't WAIT for you to show us around London, and Wales and Scotland. (We lived in Stoke on Trent at the time, and nowhere near LONDON or Wales or Scotland.) 
She was just gonna use us for free accommodation and food, and free escorted daytrips up and down the United Kingdom. I mean, it's not like I had a full time job or anything.. She just expected me to drop everything, take leave from work, and be her personal assistant/escort/cook/cleaner/bottle washer/maid.
I said it may not be convenient, and felt my face going red with anger at her fucking cheek, but she just poo-pooed me and said her and 'Steve' would be here on 17th May at around midday.
I am ashamed to say me and DH 'disappeared' on 15th and told our neighbours we were going abroad (to Spain) for a family emergency, and aren't sure when we'll back. Then we went to our parents... 3 days at mine and 3 days at his.
Then we returned on 21st May and our neighbour in the flat below, said some 'friends' of ours had come on the afternoon a couple of days after we left, with 2 suitcases each, and were banging and knocking the door for about 4-5 hours on and off.
They left at 7pm in a cab and then came back the next day, and the next. 3 days in a row, staying 4-5 hours each time, just waiting on the bench in the shared courtyard. He said we had gone abroad suddenly, but she flat out said 'I don't believe you, you're lying. They know we're coming.'
I mean what the actual FUCK? I had exchanged less than 10 letters, and been talking to her for 6-7 months, and she and her boyfriend had packed up 2 suitcases and invited themselves to OUR home. And tried desperately for 3 days to get in. Thank God we were on the 2nd floor, or they would probably have broken in through the bloody window.
The only access was the very strong upvc door with a very secure locking system, so there was no WAY they could get in! After 3 days of trying they left and never came back, and I never ever heard from her again. No loss to be fair.
'Mean thing to do' some might say. Not as mean as them thinking they can just use us for a free holiday, and expect us to drop everything and run them around and escort them like servants. When we hardly knew them and had never met them before!