Vitalik Buterin proposed Minimal Viable Plasma in 2018. When describing the functionality, he mentions the format of a UTXO plasma transaction to be

[blknum1, txindex1, oindex1, sig1, # Input 1
 blknum2, txindex2, oindex2, sig2, # Input 2
 newowner1, denom1,                # Output 1
 newowner2, denom2,                # Output 2
 fee]

This structure leads to a misunderstandings for me, which I think is best illustrated by an example:

Assume Alice owns 1 ETH and wants to send 1 ETH to Bob, who owns 4 ETH. We assume the transaction does not require any fees. She received 1 ETH from Charlie in the first (0-indexed) transaction in Block 3, where her output was 2nd. Therefore, she fills the input 1 field with (3, 0, 1, [signature of the previous 3 values with Alice's key]). Alice's second input is empty, as she does not need it to complete the transaction to Bob. The Plasma transaction Alice sends is therefore:

[3, 0, 1, (Alice's signature), # Input 1
 0, 0, 0, 0, # Input 2
 [Alice's Address], 0,                # Output 1
 [Bob's address], 5,                # Output 2
 0]

However, what happens if Alice wants to send 1 ETH to Bob, but got this through 3 transactions e.g. 0.2 ETH from Sender 1, 0.3 ETH from Sender 2 and 0.5 ETH from Sender 3? The field only allows for 2 inputs, but no combination of size 2 consisting of Alice's UTXO's allows for this, how is this addressed?