The One Direction hunk had reportedly struck up a flirty relationship with the 'Made In Chelsea' beauty - who can currently be seen on the show dating Andy Jordan - via text and Twitter messages, and last week they enjoyed an evening together.
Niall - who was recently romantically linked with model Zoe Whelan - sent a cab to pick up Louise, 22, and she stayed at his London home until the following afternoon, which meant she missed a photoshoot with Andy.
A source told The Sun newspaper: "Louise has gushed about Niall for weeks.
"She says he has the Irish gift of the gab and is very open about him being her celebrity crush.
"It started with jokey comments on Twitter, but now they text each other all the time.
"They were on the phone last week when he suggested she go over and sent a car. It was secretive and exciting."
Meanwhile, Niall, 19, enjoyed one of the "best days" of his life on Thursday when he and
bandmates Louis Tomlinson and Liam Payne trained with soccer team Real Madrid - who are managed by Jose Mourinho - during some time off from their 'Take Me Home' world tour.
He tweeted: "Up there with some of the best days of my life! Training with Real Madrid !dreams are made of that stuff
"Massive thank you on behalf of me and the lads to Real Madrid,Jose mourinho ,all the players! Unbelievable experience
All the players were really nice to us! And the gaffer I like to call him mr . Mourinho! still can't believe it! Vamos Madrid (sic)"