Sentence correction

Hi,
are the following sentences correct, please?

She has always been the one who (has) helped me.
Can we omit the "has"?

Kids were playing at/in the park.
Are both prepositions acceptable?

I placed second in the race, because Tom was running/ran real fast.
Any difference between the progressive and simple tense?

Don't even bother to come to that place, because everybody will have (already) left.
Is the future perfect correct here?

What is the shortest way to get to/reach the Tower Bridge?
Are both "get" and "reach" acceptable?

Thank you in advance!