When There’s a Monster in the Lake had a one-week run at Islington's Rosemary Branch Theatre this month, the buzz wasn’t about Tallulah Brown’s surreal exploration of dementia and loss. Instead, all eyes were on a member of the cast: one Cressida Bonas, aka Prince Harry’s ex-girlfriend, making her London stage debut as a wolf guarding the way between two worlds. Cressy and her crew raised the £2,000 for the show with a crowdfunding campaign on Kickstarter, asking the public to donate in return for rewards, including ‘a personalised poem from the devil, sent via email’ or ‘a lullaby sung to you over Skype’; £100 bought your name in the programme. But Cressida is far from the only famous face to get out the online begging bowl…