There are 1000 codes starting with 4; one possibility is to try all of them (a couple hours' work if this does not set off an anti-hacker lockdown.)

Apart from that, she can only try to think what sort of code she might have used. A visual thinker might pick one like 4268 that makes a visual pattern on the keyboard; a spatial thinker might pick one like 4586 that has a tactile pattern. A math student might pick 49-64 (two consecutive squares). Some people might pick a street number, the last four digits of a familiar phone number, or a four-letter word or name using the letters on a dial (GAIL = 4245)

Good Hunting!
RD