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Legally, there is nothing wrong with getting married while she is in the U.S. as a visitor (on a B-2 visa), if she returns home at the end of her visa-permitted stay. But that doesn't it’s risk-free strategy. It is common to use a visitor visa as a way of entering the U.S., getting married, and then applying for adjustment of status (a green card) after arrival, to avoid the longer process of applying for a fiancee or marriage-based visa from overseas.
However, in many cases, after someone obtain a visitor visa, the border official who greets them upon U.S. entry may not believe their tourist intentions, and may exercise "expedited removal" powers to deny entry and send them home. That puts an order of removal on their record, preventing a return to the U.S. for several years.
It is better to obtain a fiance visa (K-1) for travel to the United States to marry. It takes longer, about 6 months, but your entry will be easier, and there is little risk of denial of the visa, especially from England.
So yes she can get married to you while in the US while on a B-1/B-2 tourist visa, but there is the risk of denial.
I hope this helps.