Subject: Re: A strategy I read about
She claims that when you go DITM, the time premium + the strike price can be less than 1% higher than spy. Basically zero borrowing cost.

No, I suspect that her estimate is a bit crude. She probably forgot about foregoing dividends, at a guess.
Or looked at a time stretch that interest rates were pretty low. There is no such thing as free uncallable leverage.

Check a quote and check it yourself. Don't use the "last" price, though, look at midpoint of bid and ask while the market is open.
If you're buying that call for SPY, you'd probably have to pay 20% of bid + 80% of ask. Add the strike, add the dividends expected from SPY before expiry, and compare the total to the price of SPY. I'll wager the "extra" with the options works out to a lot more than 1%/year. More like 6%/year on the "borrowed" money, at a guess.

For someone wanting to go long the broad index with some leverage, and with potentially some trading, E-mini index futures would be the more obvious way to go. They are almost free to trade because of the low commissions and super tight bid/ask spreads. And there is no "extra" price built into the price for volatility: they tend to track VERY closely the current index level, plus the short term interest rate till contract expiry, minus the regular dividends expected before expiry. Futures allow much higher leverage than call options...the trick is to COMPLETELY IGNORE that opportunity and don't use much leverage, keep a lot of cash around. An index can drop by half at any time, and the cash will disappear from your account minute by minute. It might be worthwhile to buy some very deep out of the money put options as insurance against a REALLY huge drop so your cash pile is never a bit too small because of the modest leverage you're using---since that's so rare, the insurance is pretty cheap.

As for the timing, my suggestion would be not to use the scheme long/short, but long/cash. (well, my actual suggestion would be not to use the scheme, but that's a different conversation). Make a good bullish wager when the omens are good (preferably multiple omens, all of them). And just sit on your duff the rest of the time.

Jim