The first pair she loses willingly while she's chasing down a lead- or rather, as willingly as it gets; it's not that great a tragedy because while she got them on sale, she's regretted ever buying them since Clark complimented her on them. The man barely knew how to dress himself. Him having a positive opinion on a pair of shoes she purchased was dire, indeed.
She loses the second pair that week somewhere in Hobb's Bay; she would swear over it if weren't for the fact that she's trying to hide on board one of the most trashy cargo ships she's ever seen (which is saying something), and the fact that she removed them because of the impressively loud click the heels made on any surface short of mud. This pair she'll be replacing, if only because it guaranteed that the interns at the Planet ran in fear to get out of her way.
The third pair- still in the same week, no less- she loses while she's being escorted out of the main LexCorp building. Lex apparently hasn't been on a firing streak lately, because they're the same guards from last time, which means they remembered the nasty kick to the shin she gave one of them- in the same metal tipped heels- over the comments they had made. She doesn't have to replace these, because Lex has the gall to have them delivered by courier to the Daily Planet, with a signature required for delivery confirmation.
The fourth pair isn't even lost in the line of duty; the back strap gives out when she's tugging them on before work. These she bought during a weekend assignment in Gotham. Shoe shopping hadn't been planned, but she ended up going for a surprise lunch with Bruce Wayne to a fancy restaurant. Getting a replacement pair will give her an excuse to visit him, and maybe pull his attention away from Gotham's 'nightlife' for a bit. Alfred always seemed pleased when she calls, though she's made it clear that she's not interested in pursuing a solid relationship. She really doesn't want a man who lives two different lives.
When she finally gets in to work (wearing her favorite pair of red pumps- the same color as Superman's cape) she talks to Cat about the shoepocalypse since the other woman usually knows where the sales are; thankfully, Clark is already there- when she's had enough of her fill of Cat's usual gossip, she excuses herself hastily. "But I swear, if I lose another pair-Smallville! What are you waiting for? Sorry, Cat, we need to get going."
Naturally, an hour after leaving the Planet with Clark in tow, he disappears right before their interview with the owner of a demolition firm who was suspected of bribery. She waits three minutes before she opens the door- and is immediately knocked off her feet, and more importantly, out of her shoes. She registers the explosion a bit after the fact that Superman's flying her off to safety again, and that after the fact that she just lost the fifth pair of shoes that week to someone who thought blowing reporters up was an appropriate response to an interview about alleged bribery.
He sets her down on a rooftop a safe distance away from the ruined building, and before he can even finish asking if she's alright, she sees what he's holding in one of his hands. "You saved my shoes!"
She's so happy she kisses him before he -Superman!- can even react, and when it's over he's wearing the same flustered expression Clark usually gets when she's trying to cross-examine him or he's just walked into hearing range of the wrong conversation.
Superman mutters something about finding the culprit before he quickly flies off, and Lois pulls her red pumps back on.
She knew these shoes were her favorite pair for a reason.