Can I carry silver worth 2500$ from India to USA?

It is definitely not forbidden to import the items you describe. However it is your responsibility to declare items you are bringing into the country, if they are over the allowable values, and to pay duties on them. $2500 worth of silver is definitely over the allowable values, and there will be duty to pay. Failing to declare items you are importing is an offence. You will be asked the value of items you are bringing with you, either on the paper form or on the computer terminal.

It makes no difference whether the items are yours and you are giving them to your sister, or if she bought them abroad and you are bringing them to the US for her. Duty is payable in either case, and you are responsible for paying it.

If your sister did not buy the plates in the US then absolutely do not lie to customs. Doing so is a worse offence than failing to declare, and customs will want evidence of the purchase before they allow you to bring them in. Stating that you are bringing in nothing of value is also a lie and attracts similar penalties.

There are no special categories for things like silver. The amount you can bring is the total limits of gifts. Currently that is $100.

Since you ask, the worst thing that can happen is that you are arrested for smuggling and sent to jail. That is possible but unlikely, and a much more likely scenario is that the items are confiscated and you are made to pay a fine.

In theory, duty is due on goods over a relatively low limit. In my experience, the US customs seem to be uninterested in collecting duty on family property being sent to or brought in by a resident, so although you should be prepared to pay duty you may not have to pay anything, depending on circumstances such as how long your family has owned the plates.

For example, my late aunt left me her jewelry, all of which she had owned for decades. The total value was over $7,000. I am a British citizen and US resident, and brought the jewelry with me on returning from a trip to England. I filled in the customs form accurately, and was sent to secondary customs inspection. After questioning me for a few minutes, especially on whether I had bought anything new on my vacation, they decided not to collect any duty. I did have documentation with me - copies of my aunt's will, and of the valuer's report on her estate - but they did not ask to see the paperwork.

I suspect that experienced customs agents can distinguish someone who is telling the truth and has documentation to back it up from someone who is lying to them.

I strongly recommend telling the exact truth, and ideally having documentation to support it. Only claim you are returning items purchased in the US if that is what happened, and try to get sales receipts etc. to prove it.

The worst that can happen is you are caught committing a felony, lying in a customs declaration. That could happen if you declare, on a form or to a machine, that you have nothing of value and a search reveals a stack of silver plates.