Alli Sims was all smiles when she arrived at the chaotic scene surrounding Britney's home -- and had to cover her mouth to block her cheek-splitting grin!
The ambulance showed up shortly after -- led by a team of motorcycle cops to assist in Britney's transport to the UCLA Medical Center.
Alli and the Ambulance Arrive at Brit's
1/31/2008 6:29 AM PST BY TMZ STAFF
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