Lindsay Lohan -- Dear Charlie Sheen, Sorry I Never Said Thanks for the $100k

Lindsay Lohan sent a belated "thank you" card and flowers to casa de Charlie Sheen for that $100k check he gave her -- this just days after he called her out for being ungrateful.

You'll recall ... Charlie did an interview this week and put LiLo's manners on blast, claiming the actress never actually thanked him for the money he gave her. Not a text, not a phone call ... nothing.

Now sources close to Lindsay tell TMZ ... LiLo didn't mean to be rude and the reason she never got around to thanking Charlie personally is because her phone broke and she lost all her contacts -- including the actor's number.

Besides that, we're told Lindsay got distracted trying to deal with her slew of legal problems -- like getting arrested in NYC and the new criminal charges filed against her stemming from her PCH crash -- and she simply lost track of time.

But she made up for it ... we're told LiLo saw Charlie's comments and immediately fired off a "thank you" letter and a bouquet of flowers to his house ... as both an apology and show of gratitude.