By a contributing unnamed Father and Canonist:

A Canonical Defense of Father Marcel Guarnizo
As a priest and canon lawyer, I'd like in canonical terms, to revisit the controversial events surrounding the denial of Holy Communion to Barbara Johnson by Father Marcel Guarnizo. First of all, while I agree with many of the points by the very well-respected canonist Dr. Ed Peters, I believe that even with the rather limited information currently available, Father Guarnizo very possibly and correctly satisfied the conditions of canon 915 in denying Holy Communion to Barbara Johnson. Secondly, I would like to comment on Father Guarnizo's unjust "administrative leave" in light of the Code of Canon Law.
Part 1 - Canon 915 and Father Guarnizo
The first rule of interpretation in canon law is to read the canon. Canon 915 reads
"Those upon whom the penalty of excommunication or interdict has been imposed, and others who obstinately persist in manifest grave sin, are not to be admitted to Holy Communion."
As Ed Peters clearly points out, canon 915 lays an obligation on the minister distributing Holy Communion to deny Holy Communion to certain parties. Who are these parties? The first two parties are those who have been excommunicated or interdicted by imposition or declaration. The third party to be denied Holy Communion are those who fulfill all of the following three conditions, i.e., those who
1. Obstinately persist
2. in manifest
3. grave sin.
How is this canon to be interpreted? Ed Peters rightly mentions a general norm:
Can. 18 - "Laws which establish a penalty, restrict the free exercise of rights, or contain an exception from the law are subject to strict interpretation."
as well as canon 912:
Can. 912 - "Any baptized person not prohibited by law can and must be admitted to Holy Communion."
On the other hand, Father William Byrne, Secretary for Pastoral Ministry and Social Concerns, in the Archdiocese of Washington's press release, states,
"We should receive Jesus with the intention of becoming more like Him. No one is entitled to the Eucharist. It is a free gift and should be received with humility and reverence."
Ed Peters is again correct to say that the burden lies upon Father Guarnizo to prove he satisfied the requirements of canon 915. On the other hand, canon 915 lays a grave obligation on the minister of Holy Communion to protect the Eucharist from sacrilege and to prevent scandal. It goes without saying that the minister who violates canon 915 should be justly punished.
Ed Peters summarily explains why Father Guarnizo does not fufill the conditions of canon 915:
"Guarnizo did not know, and could not have verified, whether Johnson’s sin (speaking objectively), which could be grave (a conclusion I think a Catholic could reach based on the words used here) was also manifest, as well as obstinate and perseverating (sic). "
This statement raises a question. Given the extremely limited information we currently have from a variety of sources, how exactly does Ed Peters judge that Father "Guarnizo did not know, and could not have verified" Barbara Johnson was not a manifest, grave sinner? It is safe to assume that Ed Peters was not present at the chapel for the funeral, nor was he in the sacristy, nor does he have knowledge of who or how many persons witnessed the conversation that took place between Father Guarnizo and Barbara Johnson.